Indian Ocean
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The Indian Ocean is the third-largest of the world's five
ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
ic divisions, covering or ~19.8% of the
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
on
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's surface. It is bounded by
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
to the north,
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
to the west and
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
to the east. To the south it is bounded by the
Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
or
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
, depending on the definition in use. Along its core, the Indian Ocean has some large marginal or regional seas such as the
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...
,
Laccadive Sea The Laccadive Sea or Lakshadweep Sea is a body of water bordering India (including its Lakshadweep islands), the Maldives, and Sri Lanka. It is located to the southwest of Karnataka, to the west of Kerala and to the south of Tamil Nadu. This war ...
,
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
, and
Andaman Sea The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the northeastern Indian Ocean bounded by the coastlines of Myanmar and Thailand along the Gulf of Martaban and west side of the Malay Peninsula, and separated from ...
.


Etymology

The Indian Ocean has been known by its present name since at least 1515 when the Latin form ''Oceanus Orientalis Indicus'' ("Indian Eastern Ocean") is attested, named after
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, which projects into it. It was earlier known as the ''Eastern Ocean'', a term that was still in use during the mid-18th century (see map), as opposed to the ''Western Ocean'' (
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...
) before the
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
was surmised. Conversely, Chinese explorers in the Indian Ocean during the 15th century called it the Western Oceans. In
Ancient Greek geography ;Pre-Hellenistic Classical Greece *Homer * Anaximander * Hecataeus of Miletus *Massaliote Periplus *Scylax of Caryanda (6th century BC) *Herodotus ;Hellenistic period * Pytheas (died c. 310 BC) *''Periplus of Pseudo-Scylax'' (3rd or 4th century ...
, the Indian Ocean region known to the Greeks was called the
Erythraean Sea The Erythraean Sea ( grc-gre, Ἐρυθρὰ Θάλασσα, ''Erythrà Thálassa'', ."Red Sea") was a former maritime designation that always included the Gulf of Aden and at times other seas between Arabia Felix and the Horn of Africa. Origin ...
.


Geography


Extent and data

The borders of the Indian Ocean, as delineated by the
International Hydrographic Organization The International Hydrographic Organization (IHO) is an intergovernmental organisation representing hydrography. , the IHO comprised 98 Member States. A principal aim of the IHO is to ensure that the world's seas, oceans and navigable waters a ...
in 1953 included the
Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
but not the marginal seas along the northern rim, but in 2000 the IHO delimited the Southern Ocean separately, which removed waters south of 60°S from the Indian Ocean but included the northern marginal seas. Meridionally, the Indian Ocean is delimited from the
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
by the 20° east meridian, running south from
Cape Agulhas Cape Agulhas (; pt, Cabo das Agulhas , "Cape of the Needles") is a rocky headland in Western Cape, South Africa. It is the geographic southern tip of the African continent and the beginning of the dividing line between the Atlantic and Indian ...
, and from the
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
by the meridian of 146°49'E, running south from the southernmost point of
Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...
. The northernmost extent of the Indian Ocean (including marginal seas) is approximately 30° north in the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
. The Indian Ocean covers , including the
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...
and the Persian Gulf but excluding the Southern Ocean, or 19.5% of the world's oceans; its volume is or 19.8% of the world's oceans' volume; it has an average depth of and a maximum depth of . All of the Indian Ocean is in the
Eastern Hemisphere The Eastern Hemisphere is the half of the planet Earth which is east of the prime meridian (which crosses Greenwich, London, United Kingdom) and west of the antimeridian (which crosses the Pacific Ocean and relatively little land from pole to pol ...
and the centre of the Eastern Hemisphere, the
90th meridian east The meridian 90° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole. It is the border between two tropical cyclone bas ...
, passes through the
Ninety East Ridge The Ninety East Ridge (also rendered as Ninetyeast Ridge, 90E Ridge or 90°E Ridge) is a mid-ocean ridge on the Indian Ocean floor named for its near-parallel strike along the 90th meridian at the center of the Eastern Hemisphere. It is approxima ...
.


Coasts and shelves

In contrast to the Atlantic and Pacific, the Indian Ocean is enclosed by major landmasses and an archipelago on three sides and does not stretch from pole to pole, and can be likened to an embayed ocean. It is centered on the Indian Peninsula. Although this subcontinent has played a significant role in its history, the Indian Ocean has foremostly been a cosmopolitan stage, interlinking diverse regions by innovations, trade, and religion since early in human history. The
active margin Active may refer to: Music * ''Active'' (album), a 1992 album by Casiopea * Active Records, a record label Ships * ''Active'' (ship), several commercial ships by that name * HMS ''Active'', the name of various ships of the British Royal ...
s of the Indian Ocean have an average depth (land to shelf break) of with a maximum depth of . The
passive margin A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Continental rifting creat ...
s have an average depth of . The average width of the
slopes In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...
of the continental shelves are for active and passive margins respectively, with a maximum depth of . In correspondence of the
Shelf break A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
, also known as Hinge zone, the
Bouguer gravity In geodesy and geophysics, the Bouguer anomaly (named after Pierre Bouguer) is a gravity anomaly, corrected for the height at which it is measured and the attraction of terrain. The height correction alone gives a free-air gravity anomaly. Defini ...
ranges from 0 to 30 mGals that is unusual for a continental region of around 16 km thick sediments. It has been hypothesized that the "Hinge zone may represent the relict of continental and proto-oceanic crustal boundary formed during the rifting of
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
from
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
." Australia, Indonesia, and India are the three countries with the longest shorelines and exclusive economic zones. The continental shelf makes up 15% of the Indian Ocean. More than two billion people live in countries bordering the Indian Ocean, compared to 1.7 billion for the Atlantic and 2.7 billion for the Pacific (some countries border more than one ocean).


Rivers

The Indian Ocean
drainage basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, t ...
covers , virtually identical to that of the Pacific Ocean and half that of the Atlantic basin, or 30% of its ocean surface (compared to 15% for the Pacific). The Indian Ocean drainage basin is divided into roughly 800 individual basins, half that of the Pacific, of which 50% are located in Asia, 30% in Africa, and 20% in Australasia. The rivers of the Indian Ocean are shorter on average () than those of the other major oceans. The largest rivers are ( order 5) the
Zambezi The Zambezi River (also spelled Zambeze and Zambesi) is the fourth-longest river in Africa, the longest east-flowing river in Africa and the largest flowing into the Indian Ocean from Africa. Its drainage basin covers , slightly less than hal ...
,
Ganges The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian states." is ...
-
Brahmaputra The Brahmaputra is a trans-boundary river which flows through Tibet, northeast India, and Bangladesh. It is also known as the Yarlung Tsangpo in Tibetan, the Siang/Dihang River in Arunachali, Luit in Assamese, and Jamuna River in Bangla. It ...
,
Indus The Indus ( ) is a transboundary river of Asia and a trans-Himalayan river of South and Central Asia. The river rises in mountain springs northeast of Mount Kailash in Western Tibet, flows northwest through the disputed region of Kashmir, ...
,
Jubba Thawb ( ar, ثَوْب "garment"), also spelled thobe or tobe and known by various other names in different regions, is an ankle-length robe, usually with long sleeves. It is commonly worn in the Arabian Peninsula, the Middle East, North Afr ...
, and
Murray Murray may refer to: Businesses * Murray (bicycle company), an American manufacturer of low-cost bicycles * Murrays, an Australian bus company * Murray International Trust, a Scottish investment trust * D. & W. Murray Limited, an Australian who ...
rivers and (order 4) the
Shatt al-Arab The Shatt al-Arab ( ar, شط العرب, lit=River of the Arabs; fa, اروندرود, Arvand Rud, lit=Swift River) is a river of some in length that is formed at the confluence of the Euphrates and Tigris rivers in the town of al-Qurnah in ...
, Wadi Ad Dawasir (a dried-out river system on the Arabian Peninsula) and
Limpopo Limpopo is the northernmost province of South Africa. It is named after the Limpopo River, which forms the province's western and northern borders. The capital and largest city in the province is Polokwane, while the provincial legislature is ...
rivers. After the breakup of East
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
and the formation of the Himalayas, the Ganges-Brahmaputra rivers flow into the world's largest delta known as the Bengal delta or Sunderbans.


Marginal seas

Marginal seas This is a list of seas of the World Ocean, including marginal seas, areas of water, various gulfs, bights, bays, and straits. Terminology * Ocean – the four to seven largest named bodies of water in the World Ocean, all of which have "Ocean ...
, gulfs, bays and straits of the Indian Ocean include: Along the east coast of Africa, the
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channel is about lon ...
separates
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
from mainland Africa, while the
Sea of Zanj The Sea of Zanj ( ar, بحر زنج) is a former name for that portion of the western Indian Ocean adjacent to the region in the African Great Lakes referred to by medieval Arab geographers as Zanj.
is located north of Madagascar. On the northern coast of the
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...
,
Gulf of Aden The Gulf of Aden ( ar, خليج عدن, so, Gacanka Cadmeed 𐒅𐒖𐒐𐒕𐒌 𐒋𐒖𐒆𐒗𐒒) is a deepwater gulf of the Indian Ocean between Yemen to the north, the Arabian Sea to the east, Djibouti to the west, and the Guardafui Channe ...
is connected to the
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...
by the strait of
Bab-el-Mandeb The Bab-el-Mandeb (Arabic: , , ) is a strait between Yemen on the Arabian Peninsula, and Djibouti and Eritrea in the Horn of Africa. It connects the Red Sea to the Gulf of Aden. Name The strait derives its name from the dangers attendin ...
. In the Gulf of Aden, the
Gulf of Tadjoura The Gulf of Tadjoura (; ) is a gulf or basin of the Indian Ocean in the Horn of Africa. It lies south of the straits of Bab-el-Mandeb, or the entrance to the Red Sea, at . The gulf has many fishing grounds, extensive coral reefs, and abundant pea ...
is located in Djibouti and the
Guardafui Channel The Guardafui Channel ( so, Marinka Gardafuul) is an oceanic strait off the tip of the Horn of Africa that lies between the Puntland region of Somalia and Socotra to the west of the Arabian Sea. It connects the Gulf of Aden to the north with the ...
separates Socotra island from the Horn of Africa. The northern end of the Red Sea terminates in the
Gulf of Aqaba The Gulf of Aqaba ( ar, خَلِيجُ ٱلْعَقَبَةِ, Khalīj al-ʿAqabah) or Gulf of Eilat ( he, מפרץ אילת, Mifrátz Eilát) is a large gulf at the northern tip of the Red Sea, east of the Sinai Peninsula and west of the Arabian ...
and
Gulf of Suez The Gulf of Suez ( ar, خليج السويس, khalīǧ as-suwais; formerly , ', "Sea of Calm") is a gulf at the northern end of the Red Sea, to the west of the Sinai Peninsula. Situated to the east of the Sinai Peninsula is the smaller Gulf of ...
. The Indian Ocean is artificially connected to the
Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...
without ship lock through the
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popular ...
, which is accessible via the Red Sea. The Arabian Sea is connected to the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
by the
Gulf of Oman The Gulf of Oman or Sea of Oman ( ar, خليج عمان ''khalīj ʿumān''; fa, دریای عمان ''daryâ-ye omân''), also known as Gulf of Makran or Sea of Makran ( ar, خلیج مکران ''khalīj makrān''; fa, دریای مکرا ...
and the
Strait of Hormuz The Strait of Hormuz ( fa, تنگه هرمز ''Tangeh-ye Hormoz'' ar, مَضيق هُرمُز ''Maḍīq Hurmuz'') is a strait between the Persian Gulf and the Gulf of Oman. It provides the only sea passage from the Persian Gulf to the ...
. In the Persian Gulf, the
Gulf of Bahrain The Gulf of Bahrain is an inlet of the Persian Gulf on the east coast of Saudi Arabia, separated from the main body of water by the peninsula of Qatar. It surrounds the islands of Bahrain. The King Fahd Causeway crosses the western section of the ...
separates Qatar from the Arabic Peninsula. Along the west coast of India, the
Gulf of Kutch The Gulf of Kutch is located between the peninsula regions of Kutch and Saurashtra, bounded in the state of Gujarat that borders Pakistan. It opens towards the Arabian Sea facing the Osman Gulf. It is about 50 km wide at the entrance bef ...
and
Gulf of Khambat The Gulf of Khambhat, historically known as the Gulf of Cambay, is a bay on the Arabian Sea coast of India, bordering the state of Gujarat just north of Mumbai and Diu Island. The Gulf of Khambhat is about long, about wide in the north and up ...
are located in Gujarat in the northern end while the
Laccadive Sea The Laccadive Sea or Lakshadweep Sea is a body of water bordering India (including its Lakshadweep islands), the Maldives, and Sri Lanka. It is located to the southwest of Karnataka, to the west of Kerala and to the south of Tamil Nadu. This war ...
separates the Maldives from the southern tip of India. The
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
is off the east coast of India. The
Gulf of Mannar The Gulf of Mannar ( ) is a large shallow bay forming part of the Laccadive Sea in the Indian Ocean with an average depth of .
and the
Palk Strait The Palk Strait ( ta, பாக்கு நீரிணை ''Pākku Nīriṇai'', si, පෝක් සමුද්‍ර සන්ධිය ''Pok Samudra Sandhiya'') is a strait between the Tamil Nadu state of India and the Jaffna Distri ...
separates Sri Lanka from India, while the
Adam's Bridge Adam's Bridge, '; ta, ஆதாம் பாலம் ' also known as Rama's Bridge or ''Rama Setu'', '; ta, ராமர் பாலம் '; sa, रामसेतु ' is a chain of natural limestone shoals, between Pamban Island, ...
separates the two. The
Andaman Sea The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the northeastern Indian Ocean bounded by the coastlines of Myanmar and Thailand along the Gulf of Martaban and west side of the Malay Peninsula, and separated from ...
is located between the Bay of Bengal and the Andaman Islands. In Indonesia, the so-called Indonesian Seaway is composed of the
Malacca Malacca ( ms, Melaka) is a state in Malaysia located in the southern region of the Malay Peninsula, next to the Strait of Malacca. Its capital is Malacca City, dubbed the Historic City, which has been listed as a UNESCO World Heritage Site si ...
,
Sunda Sunda may refer to: Europe * Sunda, Faroe Islands India * Sunda (asura), an asura brother of Upasunda * Sunda (clan), a clan (gotra) of Jats in Haryana and Rajasthan, India Southeast Asia * Sundanese (disambiguation) ** Sundanese people ...
and
Torres Strait The Torres Strait (), also known as Zenadh Kes, is a strait between Australia and the Melanesian island of New Guinea. It is wide at its narrowest extent. To the south is Cape York Peninsula, the northernmost extremity of the Australian mai ...
s. The
Gulf of Carpentaria The Gulf of Carpentaria (, ) is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the eastern Arafura Sea (the body of water that lies between Australia and New Guinea). The northern boundary is ...
of located on the Australian north coast while the
Great Australian Bight The Great Australian Bight is a large oceanic bight, or open bay, off the central and western portions of the southern coastline of mainland Australia. Extent Two definitions of the extent are in use – one used by the International Hydrog ...
constitutes a large part of its southern coast. #
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...
- 3.862 million km2 #
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
- 2.172 million km2 #
Andaman Sea The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the northeastern Indian Ocean bounded by the coastlines of Myanmar and Thailand along the Gulf of Martaban and west side of the Malay Peninsula, and separated from ...
- 797,700 km2 #
Laccadive Sea The Laccadive Sea or Lakshadweep Sea is a body of water bordering India (including its Lakshadweep islands), the Maldives, and Sri Lanka. It is located to the southwest of Karnataka, to the west of Kerala and to the south of Tamil Nadu. This war ...
- 786,000 km2 #
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channel is about lon ...
- 700,000 km2 #
Timor Sea The Timor Sea ( id, Laut Timor, pt, Mar de Timor, tet, Tasi Mane or ) is a relatively shallow sea bounded to the north by the island of Timor, to the east by the Arafura Sea, and to the south by Australia. The sea contains a number of reefs, ...
- 610,000 km2 #
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...
- 438,000 km2 #
Gulf of Aden The Gulf of Aden ( ar, خليج عدن, so, Gacanka Cadmeed 𐒅𐒖𐒐𐒕𐒌 𐒋𐒖𐒆𐒗𐒒) is a deepwater gulf of the Indian Ocean between Yemen to the north, the Arabian Sea to the east, Djibouti to the west, and the Guardafui Channe ...
- 410,000 km2 #
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
- 251,000 km2 #
Flores Sea The Flores Sea covers of water in Indonesia. The sea is bounded on the north by the island of Celebes and on the south by Sunda Islands of Flores and Sumbawa. Geography The seas that border the Flores Sea are the Bali Sea (to the west), Java ...
- 240,000 km2 #
Molucca Sea The Molucca Sea (Indonesian: ''Laut Maluku'') is located in the western Pacific Ocean, around the vicinity of Indonesia, specifically bordered by the Indonesian Islands of Celebes (Sulawesi) to the west, Halmahera to the east, and the Sula Islan ...
- 200,000 km2 #
Oman Sea The Gulf of Oman or Sea of Oman ( ar, خليج عمان ''khalīj ʿumān''; fa, دریای عمان ''daryâ-ye omân''), also known as Gulf of Makran or Sea of Makran ( ar, خلیج مکران ''khalīj makrān''; fa, دریای مکرا ...
- 181,000 km2 #
Great Australian Bight The Great Australian Bight is a large oceanic bight, or open bay, off the central and western portions of the southern coastline of mainland Australia. Extent Two definitions of the extent are in use – one used by the International Hydrog ...
- 45,926 km2 #
Gulf of Aqaba The Gulf of Aqaba ( ar, خَلِيجُ ٱلْعَقَبَةِ, Khalīj al-ʿAqabah) or Gulf of Eilat ( he, מפרץ אילת, Mifrátz Eilát) is a large gulf at the northern tip of the Red Sea, east of the Sinai Peninsula and west of the Arabian ...
- 239 km2 #
Gulf of Khambhat The Gulf of Khambhat, historically known as the Gulf of Cambay, is a bay on the Arabian Sea coast of India, bordering the state of Gujarat just north of Mumbai and Diu Island. The Gulf of Khambhat is about long, about wide in the north and u ...
#
Gulf of Kutch The Gulf of Kutch is located between the peninsula regions of Kutch and Saurashtra, bounded in the state of Gujarat that borders Pakistan. It opens towards the Arabian Sea facing the Osman Gulf. It is about 50 km wide at the entrance bef ...
#
Gulf of Suez The Gulf of Suez ( ar, خليج السويس, khalīǧ as-suwais; formerly , ', "Sea of Calm") is a gulf at the northern end of the Red Sea, to the west of the Sinai Peninsula. Situated to the east of the Sinai Peninsula is the smaller Gulf of ...


Climate

Several features make the Indian Ocean unique. It constitutes the core of the large-scale
Tropical Warm Pool The Tropical Warm Pool (TWP) or Indo-Pacific Warm Pool is a mass of ocean water located in the western Pacific Ocean and eastern Indian Ocean which consistently exhibits the highest water temperatures over the largest expanse of the Earth's surface. ...
which, when interacting with the atmosphere, affects the climate both regionally and globally. Asia blocks heat export and prevents the ventilation of the Indian Ocean
thermocline A thermocline (also known as the thermal layer or the metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) in which temperature changes more drastically with ...
. That continent also drives the Indian Ocean
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...
, the strongest on Earth, which causes large-scale seasonal variations in ocean currents, including the reversal of the
Somali Current The Somali Current is a warm ocean boundary current that runs along the coast of Somalia and Oman in the Western Indian Ocean and is analogous to the Gulf Stream in the Atlantic Ocean. This current is heavily influenced by the monsoons and is th ...
and
Indian Monsoon Current The Indian Monsoon Current refers to the seasonally varying ocean current regime found in the tropical regions of the northern Indian Ocean. During winter, the flow of the upper ocean is directed westward from near the Indonesian Archipelago to th ...
. Because of the Indian Ocean
Walker circulation The Walker circulation, also known as the Walker cell, is a conceptual model of the air flow in the tropics in the lower atmosphere (troposphere). According to this model, parcels of air follow a closed circulation in the zonal and vertical dir ...
there are no continuous equatorial easterlies.
Upwelling Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nut ...
occurs near the
Horn of Africa The Horn of Africa (HoA), also known as the Somali Peninsula, is a large peninsula and geopolitical region in East Africa.Robert Stock, ''Africa South of the Sahara, Second Edition: A Geographical Interpretation'', (The Guilford Press; 2004), ...
and the
Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate ...
in the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
and north of the trade winds in the Southern Hemisphere. The
Indonesian Throughflow The Indonesian Throughflow (ITF; ) is an ocean current with importance for global climate as is the low-latitude movement of warm, relative freshwater from the north Pacific to the Indian Ocean. It thus serves as a main upper branch of the glob ...
is a unique Equatorial connection to the Pacific. The climate north of the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
is affected by a
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...
climate. Strong north-east winds blow from October until April; from May until October south and west winds prevail. In the Arabian Sea, the violent Monsoon brings rain to the Indian subcontinent. In the southern hemisphere, the winds are generally milder, but summer storms near Mauritius can be severe. When the monsoon winds change, cyclones sometimes strike the shores of the
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...
and the
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
. Some 80% of the total annual rainfall in India occurs during summer and the region is so dependent on this rainfall that many civilisations perished when the Monsoon failed in the past. The huge variability in the Indian Summer Monsoon has also occurred pre-historically, with a strong, wet phase 33,500–32,500 BP; a weak, dry phase 26,000–23,500 BC; and a very weak phase 17,000–15,000 BP, corresponding to a series of dramatic global events: Bølling-Allerød,
Heinrich Heinrich may refer to: People * Heinrich (given name), a given name (including a list of people with the name) * Heinrich (surname), a surname (including a list of people with the name) *Hetty (given name), a given name (including a list of peo ...
, and
Younger Dryas The Younger Dryas (c. 12,900 to 11,700 years BP) was a return to glacial conditions which temporarily reversed the gradual climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger Dryas was the last stage ...
. The Indian Ocean is the warmest ocean in the world. Long-term ocean temperature records show a rapid, continuous warming in the Indian Ocean, at about (compared to for the warm pool region) during 1901–2012. Research indicates that human induced
greenhouse warming The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...
, and changes in the frequency and magnitude of
El Niño El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date L ...
(or the
Indian Ocean Dipole The Indian Ocean Dipole (IOD), also known as the Indian Niño, is an irregular oscillation of sea surface temperatures in which the western Indian Ocean becomes alternately warmer (positive phase) and then colder (negative phase) than the eastern ...
), events are a trigger to this strong warming in the Indian Ocean. South of the Equator (20–5°S), the Indian Ocean is gaining heat from June to October, during the austral winter, while it is losing heat from November to March, during the austral summer. In 1999, the
Indian Ocean Experiment The Indian Ocean Experiment (INDOEX) was a 1999 multinational scientific study designed to measure the transport of air pollution from Southeast Asia into the Indian Ocean. The project was led by Veerabhadran Ramanathan. Findings * Plumes of sulfat ...
showed that fossil fuel and biomass burning in South and Southeast Asia caused air pollution (also known as the
Asian brown cloud The Indian Ocean brown cloud or Asian brown cloud is a layer of air pollution that recurrently covers parts of South Asia, namely the northern Indian Ocean, India, and Pakistan. Viewed from satellite photos, the cloud appears as a giant brown st ...
) that reach as far as the
Intertropical Convergence Zone The Intertropical Convergence Zone (ITCZ ), known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. It encircles Earth near the thermal e ...
at 60°S. This pollution has implications on both a local and global scale.


Oceanography

Forty percent of the sediment of the Indian Ocean is found in the Indus and Ganges fans. The oceanic basins adjacent to the continental slopes mostly contain terrigenous sediments. The ocean south of the
polar front In meteorology, the polar front is the weather front boundary between the polar cell and the Ferrel cell around the 60° latitude, near the polar regions, in both hemisphere. At this boundary a sharp gradient in temperature occurs between these ...
(roughly 50° south latitude) is high in biologic productivity and dominated by non-stratified sediment composed mostly of
siliceous Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
oozes. Near the three major mid-ocean ridges the ocean floor is relatively young and therefore bare of sediment, except for the
Southwest Indian Ridge The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...
due to its ultra-slow spreading rate. The ocean's
currents Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...
are mainly controlled by the monsoon. Two large
gyre In oceanography, a gyre () is any large system of circulating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity, horizontal friction and vertical friction dete ...
s, one in the northern hemisphere flowing clockwise and one south of the equator moving anticlockwise (including the
Agulhas Current The Agulhas Current () is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary curren ...
and
Agulhas Return Current The Agulhas Return Current (ARC) is an ocean current in the South Indian Ocean. The ARC contributes to the water exchange between oceans by forming a link between the South Atlantic Current and the South Indian Ocean Current. It can reach veloc ...
), constitute the dominant flow pattern. During the winter monsoon (November–February), however, circulation is reversed north of 30°S and winds are weakened during winter and the transitional periods between the monsoons. The Indian Ocean contains the largest submarine fans of the world, the
Bengal Fan The Bengal Fan, also known as the Ganges Fan, is the largest submarine fan on Earth. Geography It is located in Eurasia, being about long, wide with a maximum thickness of . The fan resulted from the uplift and erosion of the Himalayas and the ...
and Indus Fan, and the largest areas of slope terraces and
rift valley A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear d ...
s. The inflow of deep water into the Indian Ocean is 11  Sv, most of which comes from the
Circumpolar Deep Water Circumpolar Deep Water (CDW) is a designation given to the water mass in the Pacific and Indian oceans that is a mixing of other water masses in the region. It is characteristically warmer and saltier than the surrounding water masses, causing CD ...
(CDW). The CDW enters the Indian Ocean through the Crozet and
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
basins and crosses the
Southwest Indian Ridge The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...
at 30°S. In the
Mascarene Basin The Mascarene Basin is an oceanic basin in the western Indian Ocean. It was formed as the tectonic plate of the Indian subcontinent pulled away from the Madagascar Plate about 66–90 Mya, following the breaking up of the Gondwana supercont ...
the CDW becomes a deep
western boundary current Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents. Eastern boundary currents Eastern boundary currents are ...
before it is met by a re-circulated branch of itself, the North Indian Deep Water. This mixed water partly flows north into the Somali Basin whilst most of it flows clockwise in the Mascarene Basin where an oscillating flow is produced by
Rossby waves Rossby waves, also known as planetary waves, are a type of inertial wave naturally occurring in rotating fluids. They were first identified by Sweden-born American meteorologist Carl-Gustaf Arvid Rossby. They are observed in the atmospheres and ...
. Water circulation in the Indian Ocean is dominated by the Subtropical Anticyclonic Gyre, the eastern extension of which is blocked by the Southeast Indian Ridge and the 90°E Ridge. Madagascar and the Southwest Indian Ridge separate three cells south of Madagascar and off South Africa.
North Atlantic Deep Water North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the ...
reaches into the Indian Ocean south of Africa at a depth of and flows north along the eastern continental slope of Africa. Deeper than NADW, Antarctic Bottom Water flows from Enderby Basin to
Agulhas Basin The Agulhas Basin is an oceanic basin located south of South Africa where the South Atlantic Ocean and south-western Indian Ocean meet. Part of the African Plate, it is bounded by the Agulhas Ridge (part of the Agulhas-Falkland Fracture Zone) to ...
across deep channels (<) in the Southwest Indian Ridge, from where it continues into the
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channel is about lon ...
and Prince Edward Fracture Zone. North of 20° south latitude the minimum surface temperature is , exceeding to the east. Southward of 40° south latitude, temperatures drop quickly. The
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
contributes more than half () of the runoff water to the Indian Ocean. Mainly in summer, this runoff flows into the Arabian Sea but also south across the Equator where it mixes with fresher seawater from the
Indonesian Throughflow The Indonesian Throughflow (ITF; ) is an ocean current with importance for global climate as is the low-latitude movement of warm, relative freshwater from the north Pacific to the Indian Ocean. It thus serves as a main upper branch of the glob ...
. This mixed freshwater joins the
South Equatorial Current The South Equatorial Current are ocean currents in the Pacific, Atlantic, and Indian Ocean that flow east-to-west between the equator and about 20 degrees south. In the Pacific and Atlantic Oceans, it extends across the equator to about 5 degr ...
in the southern tropical Indian Ocean. Sea surface salinity is highest (more than 36 
PSU PSU may refer to: Organizations Military *Police Support Unit, a paramilitary wing of the Zimbabwe Republic Police *Port Security Unit, a U.S. Coast Guard expeditionary force protection unit Political parties * Parti Socialiste Unifié (disambig ...
) in the Arabian Sea because evaporation exceeds precipitation there. In the Southeast Arabian Sea salinity drops to less than 34 PSU. It is the lowest (c. 33 PSU) in the Bay of Bengal because of river runoff and precipitation. The Indonesian Throughflow and precipitation results in lower salinity (34 PSU) along the Sumatran west coast. Monsoonal variation results in eastward transportation of saltier water from the Arabian Sea to the Bay of Bengal from June to September and in westerly transport by the East India Coastal Current to the Arabian Sea from January to April. It is found that Arabian Sea warming is in response to the reduction in lower monsoon circulation in recent decades. An
Indian Ocean garbage patch __NOTOC__ The Indian Ocean garbage patch, discovered in 2010, is a marine garbage patch, a gyre of marine litter, suspended in the upper water column of the central Indian Ocean, specifically the Indian Ocean Gyre, one of the five major oceanic ...
was discovered in 2010 covering at least . Riding the southern
Indian Ocean Gyre The Indian Ocean gyre, located in the Indian Ocean, is one of the five major oceanic gyres, large systems of rotating ocean currents, which together form the backbone of the global conveyor belt. The Indian Ocean gyre is composed of two major curr ...
, this vortex of plastic garbage constantly circulates the ocean from Australia to Africa, down the
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channel is about lon ...
, and back to Australia in a period of six years, except for debris that gets indefinitely stuck in the centre of the gyre. The garbage patch in the Indian Ocean will, according to a 2012 study, decrease in size after several decades to vanish completely over centuries. Over several millennia, however, the global system of garbage patches will accumulate in the North Pacific. There are two amphidromes of opposite rotation in the Indian Ocean, probably caused by
Rossby wave Rossby waves, also known as planetary waves, are a type of inertial wave naturally occurring in rotating fluids. They were first identified by Sweden-born American meteorologist Carl-Gustaf Arvid Rossby. They are observed in the atmospheres an ...
propagation.
Iceberg An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...
s drift as far north as 55° south latitude, similar to the Pacific but less than in the Atlantic where icebergs reach up to 45°S. The volume of iceberg loss in the Indian Ocean between 2004 and 2012 was 24  Gt. Since the 1960s, anthropogenic warming of the global ocean combined with contributions of freshwater from retreating land ice causes a global rise in sea level. Sea level also increases in the Indian Ocean, except in the south tropical Indian Ocean where it decreases, a pattern most likely caused by rising levels of
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
es.


Marine life

Among the
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
oceans, the western Indian Ocean hosts one of the largest concentrations of
phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...
blooms in summer, due to the strong
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...
winds. The monsoonal wind forcing leads to a strong coastal and open ocean
upwelling Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nut ...
, which introduces nutrients into the upper zones where sufficient light is available for
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
and phytoplankton production. These phytoplankton blooms support the marine ecosystem, as the base of the marine food web, and eventually the larger fish species. The Indian Ocean accounts for the second-largest share of the most economically valuable
tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: ...
catch. Its fish are of great and growing importance to the bordering countries for domestic consumption and export. Fishing fleets from
Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
,
South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
, and
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...
also exploit the Indian Ocean, mainly for
shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...
and tuna. Research indicates that increasing ocean temperatures are taking a toll on the marine ecosystem. A study on the phytoplankton changes in the Indian Ocean indicates a decline of up to 20% in the marine plankton in the Indian Ocean, during the past six decades. The tuna catch rates have also declined 50–90% during the past half-century, mostly due to increased industrial fisheries, with the ocean warming adding further stress to the fish species. Endangered and vulnerable marine mammals and turtles: 80% of the Indian Ocean is open ocean and includes nine
large marine ecosystem Large marine ecosystems (LMEs) are regions of the world's oceans, encompassing coastal areas from river basins and estuaries to the seaward boundaries of continental shelves and the outer margins of the major ocean current systems. They are rela ...
s: the
Agulhas Current The Agulhas Current () is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary curren ...
,
Somali Coastal Current Somali may refer to: Horn of Africa * Somalis, an inhabitant or ethnicity associated with Greater Somali Region ** Proto-Somali, the ancestors of modern Somalis ** Somali culture ** Somali cuisine ** Somali language, a Cushitic language ** Somal ...
,
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...
,
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...
,
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
,
Gulf of Thailand The Gulf of Thailand, also known as the Gulf of Siam, is a shallow inlet in the southwestern South China Sea, bounded between the southwestern shores of the Indochinese Peninsula and the northern half of the Malay Peninsula. It is around in l ...
, West Central Australian Shelf, Northwest Australian Shelf, and Southwest Australian Shelf. Coral reefs cover c. . The coasts of the Indian Ocean includes beaches and intertidal zones covering and 246 larger
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...
.
Upwelling Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nut ...
areas are small but important. The hypersaline
saltern A saltern is an area or installation for making salt. Salterns include modern salt-making works (saltworks), as well as hypersaline waters that usually contain high concentrations of halophilic microorganisms, primarily haloarchaea but also oth ...
s in India covers between and species adapted for this environment, such as ''
Artemia salina ''Artemia salina'' is a species of brine shrimp – aquatic crustaceans that are more closely related to '' Triops'' and cladocerans than to true shrimp. It belongs to a lineage that does not appear to have changed much in . ''A. salina'' is na ...
'' and ''
Dunaliella salina ''Dunaliella salina'' is a type of halophile green unicellular micro-algae especially found in hypersaline environments, such as salt lakes and salt evaporation ponds. Known for its antioxidant activity because of its ability to create large ...
'', are important to bird life. Coral reefs, sea grass beds, and mangrove forests are the most productive ecosystems of the Indian Ocean — coastal areas produce 20 tones per square kilometre of fish. These areas, however, are also being urbanised with populations often exceeding several thousand people per square kilometre and fishing techniques become more effective and often destructive beyond sustainable levels while the increase in sea surface temperature spreads coral bleaching.
Mangrove A mangrove is a shrub or tree that grows in coastal saline water, saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evoluti ...
s covers in the Indian Ocean region, or almost half of the world's mangrove habitat, of which is located in Indonesia, or 50% of mangroves in the Indian Ocean. Mangroves originated in the Indian Ocean region and have adapted to a wide range of its habitats but it is also where it suffers its biggest loss of habitat. In 2016 six new animal species were identified at
hydrothermal vents A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
in the Southwest Indian Ridge: a "Hoff" crab, a "giant peltospirid" snail, a whelk-like snail, a limpet, a scaleworm and a polychaete worm. The
West Indian Ocean coelacanth The West Indian Ocean coelacanth (''Latimeria chalumnae'') (sometimes known as gombessa, African coelacanth, or simply coelacanth) is a crossopterygian, one of two extant species of coelacanth, a rare order of vertebrates more closely related t ...
was discovered in the Indian Ocean off South Africa in the 1930s and in the late 1990s another species, the
Indonesian coelacanth The Indonesian coelacanth (''Latimeria menadoensis'', Indonesian: ''raja laut'') is one of two living species of coelacanth, identifiable by its brown color. It is listed as vulnerable by the IUCN, while the other species, ''L. chalumnae'' ( We ...
, was discovered off
Sulawesi Island Sulawesi (), also known as Celebes (), is an island in Indonesia. One of the four Greater Sunda Islands, and the world's eleventh-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Mindanao and the Sulu A ...
, Indonesia. Most extant coelacanths have been found in the Comoros. Although both species represent an order of
lobe-finned fishes Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...
known from the Early Devonian (410 ) and though extinct 66 mya, they are morphologically distinct from their Devonian ancestors. Over millions of years, coelacanths evolved to inhabit different environments — lungs adapted for shallow, brackish waters evolved into gills adapted for deep marine waters.


Biodiversity

Of Earth's 36
biodiversity hotspot A biodiversity hotspot is a biogeographic region with significant levels of biodiversity that is threatened by human habitation. Norman Myers wrote about the concept in two articles in ''The Environmentalist'' in 1988 and 1990, after which the co ...
nine (or 25%) are located on the margins of the Indian Ocean. * Madagascar and the islands of the western Indian Ocean (Comoros, Réunion, Mauritius, Rodrigues, the Seychelles, and Socotra), includes 13,000 (11,600 endemic) species of plants; 313 (183) birds; reptiles 381 (367); 164 (97) freshwater fishes; 250 (249) amphibians; and 200 (192) mammals. The origin of this diversity is debated; the break-up of Gondwana can explain vicariance older than 100 mya, but the diversity on the younger, smaller islands must have required a Cenozoic dispersal from the rims of the Indian Ocean to the islands. A "reverse colonisation", from islands to continents, apparently occurred more recently; the
chameleon Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. The members of this family are best known for their distinct range of colors, bein ...
s, for example, first diversified on Madagascar and then colonised Africa. Several species on the islands of the Indian Ocean are textbook cases of evolutionary processes; the
dung beetle Dung beetles are beetles that feed on feces. Some species of dung beetles can bury dung 250 times their own mass in one night. Many dung beetles, known as ''rollers'', roll dung into round balls, which are used as a food source or breeding cha ...
s,
day gecko ''Phelsuma'' is a large genus of geckos in the Family (biology), family Gekkonidae. Species in the genus ''Phelsuma'' are commonly referred to as day geckos. Some day geckos are seriously endangered and some are common, but all ''Phelsuma'' spec ...
s, and lemurs are all examples of adaptive radiation. Many bones (250 bones per square metre) of recently extinct vertebrates have been found in the Mare aux Songes swamp in Mauritius, including bones of the Dodo bird (''Raphus cucullatus'') and ''Cylindraspis'' giant tortoise. An analysis of these remains suggests a process of aridification began in the southwest Indian Ocean began around 4,000 years ago. * Maputaland-Pondoland-Albany Hotspot, Maputaland-Pondoland-Albany (MPA); 8,100 (1,900 endemic) species of plants; 541 (0) birds; 205 (36) reptiles; 73 (20) freshwater fishes; 73 (11) amphibians; and 197 (3) mammals. Mammalian megafauna once widespread in the MPA was driven to near extinction in the early 20th century. Some species have been successfully recovered since then — the population of white rhinoceros (''Ceratotherium simum simum'') increased from less than 20 individuals in 1895 to more than 17,000 as of 2013. Other species are still dependent of fenced areas and management programs, including black rhinoceros (''Diceros bicornis minor''), African wild dog (''Lycaon pictus''), cheetah (''Acynonix jubatus''), elephant (''Loxodonta africana''), and lion (''Panthera leo''). * Coastal forests of eastern Africa; 4,000 (1,750 endemic) species of plants; 636 (12) birds; 250 (54) reptiles; 219 (32) freshwater fishes; 95 (10) amphibians; and 236 (7) mammals. This biodiversity hotspot (and namesake ecoregion and "Endemic Bird Area") is a patchwork of small forested areas, often with a unique assemblage of species within each, located within from the coast and covering a total area of c. . It also encompasses coastal islands, including Zanzibar and Pemba, and Mafia. *
Horn of Africa The Horn of Africa (HoA), also known as the Somali Peninsula, is a large peninsula and geopolitical region in East Africa.Robert Stock, ''Africa South of the Sahara, Second Edition: A Geographical Interpretation'', (The Guilford Press; 2004), ...
; 5,000 (2,750 endemic) species of plants; 704 (25) birds; 284 (93) reptiles; 100 (10) freshwater fishes; 30 (6) amphibians; and 189 (18) mammals. This area, one of the only two hotspots that are entirely arid, includes the Ethiopian Highlands, the East African Rift, East African Rift valley, the Socotra islands, as well as some small islands in the Red Sea and areas on the southern Arabic Peninsula. Endemic and threatened mammals include the dibatag (''Ammodorcas clarkei'') and Speke's gazelle (''Gazella spekei''); the Somali wild ass (''Equus africanus somaliensis'') and hamadryas baboon (''Papio hamadryas''). It also contains many reptiles. In Somalia, the centre of the hotspot, the landscape is dominated by Acacia-Commiphora deciduous bushland, but also includes the Yeheb nut (''Cordeauxia edulus'') and species discovered more recently such as the Somali cyclamen (''Cyclamen somalense''), the only cyclamen outside the Mediterranean. Warsangli linnet (''Carduelis johannis'') is an endemic bird found only in northern Somalia. An unstable political situation and mismanagement has resulted in overgrazing which has produced one of the most degraded hotspots where only c. 5 % of the original habitat remains. * The Western Ghats–Sri Lanka; 5,916 (3,049 endemic) species of plants; 457 (35) birds; 265 (176) reptiles; 191 (139) freshwater fishes; 204 (156) amphibians; and 143 (27) mammals. Encompassing the west coast of India and Sri Lanka, until c. 10,000 years ago a landbridge connected Sri Lanka to the Indian Subcontinent, hence this region shares a common community of species. * Indo-Burma; 13.500 (7,000 endemic) species of plants; 1,277 (73) birds; 518 (204) reptiles; 1,262 (553) freshwater fishes; 328 (193) amphibians; and 401 (100) mammals. Indo-Burma encompasses a series of mountain ranges, five of Asia's largest river systems, and a wide range of habitats. The region has a long and complex geological history, and long periods sea level rise, rising sea levels and glaciations have isolated ecosystems and thus promoted a high degree of endemism and speciation. The region includes two centres of endemism: the Annamite Mountains and the northern highlands on the China-Vietnam border. Several distinct floristic regions, the Indian, Malesian, Sino-Himalayan, and Indochinese regions, meet in a unique way in Indo-Burma and the hotspot contains an estimated 15,000–25,000 species of vascular plants, many of them endemic. * Sundaland; 25,000 (15,000 endemic) species of plants; 771 (146) birds; 449 (244) reptiles; 950 (350) freshwater fishes; 258 (210) amphibians; and 397 (219) mammals. Sundaland encompasses 17,000 islands of which Borneo and Sumatra are the largest. Endangered mammals include the Bornean orangutan, Bornean and Sumatran orangutans, the proboscis monkey, and the Javan rhinoceros, Javan and Sumatran rhinoceroses. * Wallacea; 10,000 (1,500 endemic) species of plants; 650 (265) birds; 222 (99) reptiles; 250 (50) freshwater fishes; 49 (33) amphibians; and 244 (144) mammals. * Southwest Australia (ecoregion), Southwest Australia; 5,571 (2,948 endemic) species of plants; 285 (10) birds; 177 (27) reptiles; 20 (10) freshwater fishes; 32 (22) amphibians; and 55 (13) mammals. Stretching from Shark Bay to Israelite Bay and isolated by the arid Nullarbor Plain, the southwestern corner of Australia is a floristic region with a stable climate in which one of the world's largest floral biodiversity and an 80% endemism has evolved. From June to September it is an explosion of colours and the Wildflower Festival in Perth in September attracts more than half a million visitors.


Geology

As the youngest of the major oceans, the Indian Ocean has active spreading ridges that are part of the worldwide system of mid-ocean ridges. In the Indian Ocean these spreading ridges meet at the Rodrigues Triple Point with the Central Indian Ridge, including the Carlsberg Ridge, separating the African Plate from the Indian Plate; the
Southwest Indian Ridge The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...
separating the African Plate from the Antarctic Plate; and the Southeast Indian Ridge separating the Australian Plate from the Antarctic Plate. The Central Indian Ridge is intercepted by the Owen Fracture Zone. Since the late 1990s, however, it has become clear that this traditional definition of the Indo-Australian Plate cannot be correct; it consists of three plates — the Indian Plate, the Capricorn Plate, and Australian Plate — separated by diffuse boundary zones. Since 20 Ma the African Plate is being divided by the East African Rift System into the Nubian Plate, Nubian and Somali Plate, Somalia plates. There are only two trenches in the Indian Ocean: the -long Java Trench between Java and the Sunda Trench and the -long Makran Trench south of Iran and Pakistan. A series of ridges and seamount chains produced by Hotspot (geology), hotspots pass over the Indian Ocean. The Réunion hotspot (active 70–40 million years ago) connects Réunion and the Mascarene Plateau to the Chagos-Laccadive Ridge and the Deccan Traps in north-western India; the Kerguelen hotspot (100–35 million years ago) connects the Kerguelen Islands and Kerguelen Plateau to the
Ninety East Ridge The Ninety East Ridge (also rendered as Ninetyeast Ridge, 90E Ridge or 90°E Ridge) is a mid-ocean ridge on the Indian Ocean floor named for its near-parallel strike along the 90th meridian at the center of the Eastern Hemisphere. It is approxima ...
and the Rajmahal Traps in north-eastern India; the Marion hotspot (100–70 million years ago) possibly connects Prince Edward Islands to the Eighty Five East Ridge. These hotspot tracks have been broken by the still active spreading ridges mentioned above. There are fewer seamounts in the Indian Ocean than in the Atlantic and Pacific. These are typically deeper than and located north of 55°S and west of 80°E. Most originated at spreading ridges but some are now located in basins far away from these ridges. The ridges of the Indian Ocean form ranges of seamounts, sometimes very long, including the Carlsberg Ridge, Madagascar Ridge, Central Indian Ridge,
Southwest Indian Ridge The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...
, Chagos-Laccadive Ridge, Eighty Five East Ridge, 85°E Ridge, Ninety East Ridge, 90°E Ridge, Southeast Indian Ridge, Broken Ridge, and East Indiaman Ridge. The Agulhas Plateau and Mascarene Plateau are the two major shallow areas. The opening of the Indian Ocean began 156  when Africa separated from East
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
. The Indian Subcontinent began to separate from Australia-Antarctica 135–125 Ma and as the Tethys Ocean north of India began to close 118–84 Ma the Indian Ocean opened behind it.


History

The Indian Ocean, together with the Mediterranean, has connected people since ancient times, whereas the Atlantic and Pacific have had the roles of barriers or ''Terra incognita, mare incognitum''. The written history of the Indian Ocean, however, has been Eurocentrism, Eurocentric and largely dependent on the availability of written sources from the colonial era. This history is often divided into an ancient period followed by an Islamic period; the subsequent periods are often subdivided into Portuguese Empire, Portuguese, Dutch Empire, Dutch, and British Empire, British periods. A concept of an "Indian Ocean World" (IOW), similar to that of the "Atlantic World", exists but emerged much more recently and is not well established. The IOW is, nevertheless, sometimes referred to as the "first global economy" and was based on the monsoon which linked Asia, China, India, and Mesopotamia. It developed independently from the European global trade in the Mediterranean and Atlantic and remained largely independent from them until European 19th-century colonial dominance. The diverse history of the Indian Ocean is a unique mix of cultures, ethnic groups, natural resources, and shipping routes. It grew in importance beginning in the 1960s and 1970s and, after the Cold War, it has undergone periods of political instability, most recently with the emergence of India and China as regional powers.


First settlements

Pleistocene fossils of ''Homo erectus'' and other pre–''H. sapiens'' hominid fossils, similar to ''Homo heidelbergensis, H. heidelbergensis'' in Europe, have been found in India. According to the Toba catastrophe theory, a supereruption c. 74,000 years ago at Lake Toba, Sumatra, covered India with volcanic ashes and wiped out one or more lineages of such archaic humans in India and Southeast Asia. The Recent African origin of modern humans, ''Out of Africa'' theory states that ''Homo sapiens'' spread from Africa into mainland Eurasia. The more recent ''Southern Dispersal'' or ''Coastal hypothesis'' instead advocates that modern humans spread along the coasts of the Arabic Peninsula and southern Asia. This hypothesis is supported by Mitochondrial DNA, mtDNA research which reveals a rapid dispersal event during the Late Pleistocene (11,000 years ago). This coastal dispersal, however, began in East Africa 75,000 years ago and occurred intermittently from estuary to estuary along the northern perimeter of the Indian Ocean at a rate of per year. It eventually resulted in modern humans migrating from Sundaland, Sunda over Wallacea to Australia (continent), Sahul (Southeast Asia to Australia). Since then, waves of migration have resettled people and, clearly, the Indian Ocean littoral had been inhabited long before the first civilisations emerged. 5000–6000 years ago six distinct cultural centres had evolved around the Indian Ocean: East Africa, the Middle East, the Indian Subcontinent, South East Asia, the Malay World, and Australia; each interlinked to its neighbours. Food globalisation began on the Indian Ocean littoral c. 4.000 years ago. Five African crops — Sorghum bicolor, sorghum, Pennisetum glaucum, pearl millet, Eleusine coracana, finger millet, Vigna unguiculata, cowpea, and Lablab purpureus, hyacinth bean — somehow found their way to Gujarat in India during the Late Harappan (2000–1700 BCE). Gujarati merchants evolved into the first explorers of the Indian Ocean as they traded African goods such as ivory, tortoise shells, and slaves. Panicum miliaceum, Broomcorn millet found its way from Central Asia to Africa, together with chicken and zebu cattle, although the exact timing is disputed. Around 2000 BCE Piper nigrum, black pepper and Sesamum indicum, sesame, both native to Asia, appear in Egypt, albeit in small quantities. Around the same time the Rattus rattus, black rat and the Mus musculus, house mouse emigrate from Asia to Egypt. Banana reached Africa around 3000 years ago. At least eleven prehistoric tsunamis have struck the Indian Ocean coast of Indonesia between 7400 and 2900 years ago. Analysing sand beds in caves in the Aceh region, scientists concluded that the intervals between these tsunamis have varied from series of minor tsunamis over a century to dormant periods of more than 2000 years preceding megathrusts in the Sunda Trench. Although the risk for future tsunamis is high, a major megathrust such as the one in 2004 is likely to be followed by a long dormant period. A group of scientists have argued that two large-scale impact events have occurred in the Indian Ocean: the Burckle Crater in the southern Indian Ocean in 2800 BCE and the Kanmare and Tabban craters in the
Gulf of Carpentaria The Gulf of Carpentaria (, ) is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the eastern Arafura Sea (the body of water that lies between Australia and New Guinea). The northern boundary is ...
in northern Australia in 536 CE. Evidences for these impacts, the team argue, are micro-ejecta and Chevron (land form), Chevron dunes in southern Madagascar and in the Australian gulf. Geological evidences suggest the tsunamis caused by these impacts reached above sea level and inland. The impact events must have disrupted human settlements and perhaps even contributed to Extreme weather events of 535–536, major climate changes.


Antiquity

The history of the Indian Ocean is marked by maritime trade; cultural and commercial exchange probably date back at least seven thousand years. Human culture spread early on the shores of the Indian Ocean and was always linked to the cultures of the Mediterranean and the Persian Gulf. Before c. 2000 BCE, however, cultures on its shores were only loosely tied to each other; bronze, for example, was developed in Mesopotamia c. 3000 BCE but remained uncommon in Egypt before 1800 BCE. During this period, independent, short-distance oversea communications along its littoral margins evolved into an all-embracing network. The début of this network was not the achievement of a centralised or advanced civilisation but of local and regional exchange in the Persian Gulf, the Red Sea, and the Arabian Sea. Sherds of Ubaid period, Ubaid (2500–500 BCE) pottery have been found in the western Gulf at Dilmun, present-day Bahrain; traces of exchange between this trading centre and Mesopotamia. The Sumerians traded grain, pottery, and bitumen (used for reed boats) for copper, stone, timber, tin, dates, onions, and pearls. Coast-bound vessels transported goods between the Indus Valley civilisation (2600–1900 BCE) in the Indian subcontinent (modern-day Pakistan and Northwest India) and the Persian Gulf and Egypt. The Red Sea, one of the main trade routes in Antiquity, was explored by First Dynasty of Egypt, Egyptians and Phoenicians during the last two millennia BCE. In the 6th century, BCE Greek explorer Scylax of Caryanda made a journey to India, working for the Persian king Darius the Great, Darius, and his now-lost account put the Indian Ocean on the maps of Greek geographers. The Greeks began to explore the Indian Ocean following the conquests of Alexander the Great, who ordered a circumnavigation of the Arabian Peninsula in 323 BCE. During the two centuries that followed the reports of the explorers of Ptolemaic Kingdom, Ptolemaic Egypt resulted in the best maps of the region until the Portuguese era many centuries later. The main interest in the region for the Ptolemies was not commercial but military; they explored Africa to hunt for war elephants. The Rub' al Khali desert isolates the southern parts of the Arabic Peninsula and the Indian Ocean from the Arabic world. This encouraged the development of maritime trade in the region linking the Red Sea and the Persian Gulf to East Africa and India. The
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...
(from ''mawsim'', the Arabic word for season), however, was used by sailors long before being "discovered" by Hippalus in the 1st century. Indian wood have been found in Sumerian cities, there is evidence of Akkad coastal trade in the region, and contacts between India and the Red Sea dates back to 2300 B.C. The archipelagoes of the central Indian Ocean, the Laccadive and Maldive islands, were probably populated during the 2nd century B.C. from the Indian mainland. They appear in written history in the account of merchant Sulaiman al-Tajir in the 9th century but the treacherous reefs of the islands were most likely cursed by the sailors of Aden long before the islands were even settled. ''Periplus of the Erythraean Sea'', an Alexandrian guide to the world beyond the Red Sea — including Africa and India — from the first century CE, not only gives insights into trade in the region but also shows that Roman and Greek sailors had already gained knowledge about the
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...
winds. The contemporaneous settlement of
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
by Austronesian people, Austronesian sailors shows that the littoral margins of the Indian Ocean were being both well-populated and regularly traversed at least by this time. Albeit the monsoon must have been common knowledge in the Indian Ocean for centuries. The Indian Ocean's relatively calmer waters opened the areas bordering it to trade earlier than the Atlantic or Pacific oceans. The powerful monsoons also meant ships could easily sail west early in the season, then wait a few months and return eastwards. This allowed ancient Indonesian peoples to cross the Indian Ocean to settle in
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
around 1 CE. In the 2nd or 1st century BCE, Eudoxus of Cyzicus was the first Greece, Greek to cross the Indian Ocean. The probably fictitious sailor Hippalus is said to have learnt the direct route from Arabia to India around this time. During the 1st and 2nd centuries AD intensive Roman commerce, trade relations developed between Roman Egypt and the Tamil people, Tamil kingdoms of the Chera Dynasty, Cheras, Chola Dynasty, Cholas and Pandyas in South India, Southern India. Like the Indonesian people above, the western sailors used the monsoon to cross the ocean. The unknown author of the ''Periplus of the Erythraean Sea'' describes this route, as well as the commodities that were traded along various commercial ports on the coasts of the Horn of Africa and India circa 1 CE. Among these trading settlements were Mosylon and Opone on the Red Sea littoral.


Age of Discovery

Unlike the Pacific Ocean where the civilization of the Polynesians reached most of the far-flung islands and atolls and populated them, almost all the islands, archipelagos and atolls of the Indian Ocean were uninhabited until colonial times. Although there were numerous ancient civilizations in the coastal states of Asia and parts of Africa, the Maldives were the only island group in the Central Indian Ocean region where an ancient civilization flourished. Dhivehi people, Maldivians, on their annual trade trip, took their oceangoing trade ships to Sri Lanka rather than mainland India, which is much closer, because their ships were dependent of the
Indian Monsoon Current The Indian Monsoon Current refers to the seasonally varying ocean current regime found in the tropical regions of the northern Indian Ocean. During winter, the flow of the upper ocean is directed westward from near the Indonesian Archipelago to th ...
. Arabic missionaries and merchants began to Spread of Islam#East Africa, spread Islam along the western shores of the Indian Ocean from the 8th century, if not earlier. A Swahili culture, Swahili stone mosque dating to the 8th–15th centuries has been found in Shanga, Pate Island, Shanga, Kenya. Trade across the Indian Ocean gradually introduced Arabic script and rice as a Staple food, staple in Eastern Africa. Muslim merchants traded an estimated 1000 African slaves annually between 800 and 1700, a number that grew to during the 18th century, and 3700 during the period 1800–1870. Slave trade also occurred in the eastern Indian Ocean before the Dutch settled there around 1600 but the volume of this trade is unknown. From 1405 to 1433 admiral Zheng He said to have led large fleets of the Ming Dynasty on several treasure voyages through the Indian Ocean, ultimately reaching the coastal countries of East Africa. The Portuguese navigator Vasco da Gama rounded the Cape of Good Hope during his first voyage in 1497 and became the first European to sail to India. The Swahili people he encountered along the African east coast lived in a series of cities and had established trade routes to India and to China. Among them, the Portuguese kidnapped most of their pilots in coastal raids and onboard ships. A few of the pilots, however, were gifts by local Swahili rulers, including the sailor from Gujarat, a gift by a Malindi ruler in Kenya, who helped the Portuguese to reach India. In expeditions after 1500, the Portuguese attacked and colonised cities along the African coast. European slave trade in the Indian Ocean began when Portugal established Portuguese India, Estado da Índia in the early 16th century. From then until the 1830s, slaves were exported from Mozambique annually and similar figures has been estimated for slaves brought from Asia to the Philippines during the Iberian Union (1580–1640). The Ottoman Empire began its expansion into the Indian Ocean in 1517 with the conquest of Egypt under Sultan Selim I. Although the Ottomans shared the same religion as the trading communities in the Indian Ocean the region was unexplored by them. Maps that included the Indian Ocean had been produced by Muslim geographers centuries before the Ottoman conquests; Muslim scholars, such as Ibn Battuta in the 14th Century, had visited most parts of the known world; contemporarily with Vasco da Gama, Arab navigator Ahmad ibn Mājid had compiled a guide to navigation in the Indian Ocean; the Ottomans, nevertheless, began their own parallel era of discovery which rivalled the European expansion. The establishment of the Dutch East India Company in the early 17th century lead to a quick increase in the volume of the slave trade in the region; there were perhaps up to slaves in various Dutch Empire, Dutch colonies during the 17th and 18th centuries in the Indian Ocean. For example, some 4000 African slaves were used to build the Fort (Colombo), Colombo fortress in Dutch Ceylon. Bali and neighbouring islands supplied regional networks with slaves 1620–1830. Indian and Chinese slave traders supplied Dutch Indonesia with perhaps slaves during the 17th and 18th centuries. The East India Company (EIC) was established during the same period and in 1622 one of its ships carried slaves from the Coromandel Coast to Dutch East Indies. The EIC mostly traded in African slaves but also some Asian slaves purchased from Indian, Indonesian and Chinese slave traders. The French established colonies on the islands of Réunion and Mauritius in 1721; by 1735 some 7,200 slaves populated the Mascarene Islands, a number which had reached in 1807. The United Kingdom of Great Britain and Ireland, British captured the islands in 1810, however, and because the British had Slave Trade Act 1807, prohibited the slave trade in 1807 a system of clandestine slave trade developed to bring slaves to French planters on the islands; in all – slaves were exported to the Mascarene Islands from 1670 until 1848. In all, European traders exported – slaves within the Indian Ocean between 1500 and 1850 and almost that same amount were exported from the Indian Ocean to the Americas during the same period. Slave trade in the Indian Ocean was, nevertheless, very limited compared to slaves exported across the Atlantic.


Modern era

Scientifically, the Indian Ocean remained poorly explored before the International Indian Ocean Expedition in the early 1960s. However, the Challenger expedition, ''Challenger'' expedition 1872–1876 only reported from south of the polar front. The Valdivia Expedition, ''Valdivia'' expedition 1898–1899 made deep samples in the Indian Ocean. In the 1930s, the John Murray Expedition mainly studied shallow-water habitats. The Albatross expedition, Swedish Deep Sea Expedition 1947–1948 also sampled the Indian Ocean on its global tour and the Danish Galathea expeditions, ''Galathea'' sampled deep-water fauna from Sri Lanka to South Africa on its second expedition 1950–1952. The Soviet research vessel RV Vityaz (1939), ''Vityaz'' also did research in the Indian Ocean. The
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popular ...
opened in 1869 when the Industrial Revolution dramatically changed global shipping – the sailing ship declined in importance as did the importance of European trade in favour of trade in East Asia and Australia. The construction of the canal introduced many non-indigenous species into the Mediterranean. For example, the goldband goatfish (''Upeneus moluccensis'') has replaced the red mullet (''Mullus barbatus''); since the 1980s huge swarms of scyphozoan jellyfish (''Rhopilema nomadica'') have affected tourism and fisheries along the Levantian coast and clogged power and desalination plants. Plans announced in 2014 to Suez Canal Area Development Project, build a new, much larger Suez Canal parallel to the 19th-century canal will most likely boost the economy in the region but also cause ecological damage in a much wider area. Throughout the colonial era, islands such as Mauritius were important shipping nodes for the Dutch, French, and British. Mauritius, an inhabited island, became populated by slaves from Africa and Indian indenture system, indenture labour from India. The end of Indian Ocean in World War II, World War II marked the end of the colonial era. The British left Mauritius in 1974 and with 70% of the population of Indian descent, Mauritius became a close ally of India. In the 1980s, during the Cold War, the South African regime acted to destabilise several island nations in the Indian Ocean, including the Seychelles, Comoros, and Madagascar. India intervened in Mauritius to prevent a coup d'état, backed up by the United States who feared the Soviet Union could gain access to Port Louis and threaten the U.S. base on Diego Garcia. Iranrud is an unrealised plan by Iran and the Soviet Union to build a canal between the Caspian Sea and the Persian Gulf. Testimonies from the colonial era are stories of African slaves, Indian indentured labourers, and white settlers. But, while there was a clear racial line between free men and slaves in the Atlantic World, this delineation is less distinct in the Indian Ocean — there were Indian slaves and settlers as well as black indentured labourers. There were also a string of prison camps across the Indian Ocean, such as Cellular Jail in the Andamans, in which prisoners, exiles, POWs, forced labourers, merchants, and people of different faiths were forcefully united. On the islands of the Indian Ocean, therefore, a trend of creolisation emerged. On 26 December 2004 fourteen countries around the Indian Ocean were hit by a wave of tsunamis caused by the 2004 Indian Ocean earthquake. The waves radiated across the ocean at speeds exceeding , reached up to in height, and resulted in an estimated 236,000 deaths. In the late 2000s, the ocean evolved into a hub of Piracy in Somalia, pirate activity. By 2013, attacks off the Horn region's coast had steadily declined due to active private security and international navy patrols, especially by the Indian Navy. Malaysian Airlines Flight 370, a Boeing 777 airliner with 239 persons on board, disappeared on 8 March 2014 and is alleged to have crashed into the southern Indian Ocean about from the coast of southwest Western Australia. Despite an extensive search, the whereabouts of the remains of the aircraft is unknown. The Sentinelese people of North Sentinel Island, which lies near South Andaman Island in the Bay of Bengal, have been called by experts the most Uncontacted peoples, isolated people in the world. The sovereignty of the Chagos Archipelago in the Indian Ocean is Chagos Archipelago sovereignty dispute, disputed between the United Kingdom and Mauritius. In February 2019, the International Court of Justice in The Hague issued an advisory opinion Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965, stating that the UK must transfer the Chagos Archipelago to Mauritius. On 26 February 2022, an AB Aviation Flight 1103 Cessna 208 crashed into Indian Ocean, killing all 14 on board.


Trade

The sea lanes in the Indian Ocean are considered among the most strategically important in the world with more than 80 percent of the world's seaborne trade in oil transits through the Indian Ocean and its vital chokepoints, with 40 percent passing through the Strait of Hormuz, 35 percent through the Strait of Malacca and 8 percent through the Bab el-Mandab Strait. The Indian Ocean provides major sea routes connecting the Middle East, Africa, and East Asia with Europe and the Americas. It carries a particularly heavy traffic of petroleum and petroleum products from the oil fields of the Persian Gulf and Indonesia. Large reserves of hydrocarbons are being tapped in the offshore areas of Saudi Arabia, Iran, India, and Western Australia. An estimated 40% of the world's offshore oil production comes from the Indian Ocean. Beach sands rich in heavy minerals, and offshore placer deposits are actively exploited by bordering countries, particularly India, Pakistan, South Africa, Indonesia, Sri Lanka, and Thailand. In particular, the maritime part of the Silk Road leads through the Indian Ocean on which a large part of the global container trade is carried out. The Silk Road runs with its connections from the Chinese coast and its large container ports to the south via Hanoi to Jakarta, Singapore and Kuala Lumpur through the Strait of Malacca via the Sri Lankan Colombo opposite the southern tip of India via Malé, the capital of the Maldives, to the East African Mombasa, from there to Djibouti, then through the Red Sea over the
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popular ...
into the Mediterranean, there via Haifa, Istanbul and Athens to the Upper Adriatic to the northern Italian junction of Trieste with its international free port and its rail connections to Central Europe, Central and Eastern Europe. The Silk Road has become internationally important again on the one hand through European integration, the end of the Cold War and free world trade and on the other hand through Chinese initiatives. Chinese companies have made investments in several Indian Ocean ports, including Gwadar, Hambantota, Colombo and Sonadia. This has sparked a debate about the strategic implications of these investments. There are also Chinese investments and related efforts to intensify trade in East Africa and in European ports such as Piraeus and Trieste.Guido Santevecchi: Di Maio e la Via della Seta: «Faremo i conti nel 2020», siglato accordo su Trieste in Corriere della Sera, 5 November 2019.


See also

*
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
*
Erythraean Sea The Erythraean Sea ( grc-gre, Ἐρυθρὰ Θάλασσα, ''Erythrà Thálassa'', ."Red Sea") was a former maritime designation that always included the Gulf of Aden and at times other seas between Arabia Felix and the Horn of Africa. Origin ...
* Indo-Pacific * Indian Ocean in World War II * Indian Ocean literature * Indian Ocean Naval Symposium * Indian Ocean Research Group * Indian Ocean slave trade * List of islands in the Indian Ocean * List of ports and harbours of the Indian Ocean * List of sovereign states and dependent territories in the Indian Ocean * Indian Ocean Rim Association * Maritime Silk Road *
Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
* Territorial claims in Antarctica


References


Notes


Sources

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Further reading

* Bahl, Christopher D. "Transoceanic Arabic historiography: sharing the past of the sixteenth-century western Indian Ocean." ''Journal of Global History'' 15.2 (2020): 203–223. * Palat, Ravi. ''The Making of an Indian Ocean World-Economy, 1250–1650: Princes, Paddy fields, and Bazaars'' (2015) * Pearson, Michael (2015). ''Trade, Circulation, and Flow in the Indian Ocean World'' (Palgrave Series in Indian Ocean World Studies), . * Schnepel, Burkhard and Edward A. Alpers, eds. ''Connectivity in Motion: Island Hubs in the Indian Ocean World'' (2017). * Schottenhammer, Angela, ed. ''Early Global Interconnectivity across the Indian Ocean World, Volume I: Commercial Structures and Exchanges'' (2019) * Schottenhammer, Angela, ed. ''Early Global Interconnectivity across the Indian Ocean World, Volume II: Exchange of Ideas, Religions, and Technologies'' (2019) * Serels, Steven, ed. ''The Impoverishment of the African Red Sea Littoral, 1640–1945'' (2018)


External links

* * * {{Authority control Indian Ocean, Oceans East Africa South Asia Western Asia Landforms of the Indian Ocean, Oceans surrounding Antarctica